(1) Field of the Invention
The invention relates to a heat exchanger comprising a plurality of flat tubes for heat exchange between a first fluidum flowing inside said tubes and a second fluidum flowing outside of said tubes, a pair of manifolds connected to the end of the flat tubes and provider with an inlet and an outlet for introducing the first fluidum into the flat tubes and for discharging therefrom, each manifold being provided with at least two parallel channels, at least part of the walls of the channel having a curved surface.
(2) Description of the Related Art
Such a heat exchanger is known from WO-A-9851983.
In this known heat exchanger the manifolds are composed of a number of parallel tubes with circular cross-sections, each pair of adjacent tubes having a common wall portion, in such a way that the tubes of each manifold constitute a flat array of tubes. The circular cross-section of the tubes is selected because the high pressure inside the tubes, such as is common in modern heat exchangers used in cars and based upon CO2. It is common then to use a pressure well above 100 bar and the use of round cross-section channels avoid that stresses are built up in the walls of the manifold. Using round cross-section allows the inner wall to be thinner thereby saving weight and increasing heat transfer.
Otherwise a flat tube has to be inserted through holes, in one flat side of the manifold in order to have communication between the tubes and the manifolds. In order to have the least possible flow restriction it is preferred to insert the end portion of the flat tubes up to half way into the diameter of the channels in the manifold, as in this way the part of the end face of the flat tubes blocked by the partition walls in the manifold is minimal. However, in this way half of each channels in the manifold is blocked causing flow restriction in that part of the heat exchanger. As a compromise the end part of the flat tubes is not inserted up to half the diameter of the channels, but to about one third of the diameter. In this way the blockage in the channels of the manifold is substantially reduced, whereas the blockage of the end face of the flat tubes is only slightly increased and kept within acceptable limits.
However the disturbance of the fluid flow inside the heat exchanger, and especially inside the manifold channel is still highly disturbed by the inserted end portion of the flat tubes, which especially in high pressure systems can cause substantial pressure drops.